Single-relay line circuit



July 22, 1958 A. HEMEL SINGLE-RELAY LINE CIRCUIT Filed May 23. 19552,844,654 SINGLE-RELAY LlNE CIRCUIT Albert Hemel, Skokie, Ill., assignorto Intematonal Telephone and Telegraph Corporation, New York, N. Y., acorporation of Maryland Application May 2s, 195s, serial No. 510,427

' 11 claims. (ci. 179-18) vThis invention relates to a single-relay linecircuit particularly for the two-wire lines used in switching systems.Its principal object is to provide a satisfactory and reliable linecircuit wherein a single individual relay is employed while retainingthe general operational features -ordinarily requiring both a line relayand a cutoff relay for each line.

In carrying out the stated principal object, each two- Wire line isprovided only with an individual cutoi relay, and arelatively smallnumber of line relays are provided, each common to all of the lines of agroup. In prior attempts of this nature, any common line relay has beensubject to false operation by cumulative line leakage, particularlyleakage to ground, if placed between the ungrounded pole of the exchangebattery and the associated lines; and it has been subject to operationalfailures, by being effectively shunted out of circuit by a heavy leakageto ground on any associated line, if placed in series with the grounded.pole of the exchange battery.

According to the invention, any common line relay is placed between theground-return wires of the associated lines and the grounded pole of theexchange battery to avoid false operations responsive to line leakage toground, `and the ground-return wires of the associated lines areeffectively isolated from each other by respective impedance devicesindividually connected serially therein, whereby the common line relayis still operable, over any other associated line, in spite of a falseground connection to the ground-return wire on any associated line.Preferably, any such isolating impedance device either comprises orincludes a rectiiier element so poled ice an embodiment of the inventiontaken in conjunction with the accompanying drawing wherein a group ofline equipments and associated common tens relay is shown, together witha portion of the line finder controller of the noted Leonardapplication.

For convenience in description, the present system is assumed to have100 telephone lines, although it will be as to prevent thepotential-drop developed across the common line relay by a callingcondition on one line from being dissipated by a leak current to groundover the ground-return conductor of any other associated line.

Further, according to the invention, a local arrangement is provided fortemporarily restoring any operated common line relay after responsiveline-extension action has occurred to insure that it does not give afalse calling indication by being held operated by cross-line leakagecurrents below operate value. y

It has been chosen to illustrate the invention as applied to aline-finder controller such as disclosed in the U. S. patent application`of E. J. Leonard for a Crossbar-Switch Line-Finder System, Serial No.468,443, led November 12, 1954. In such application, the controllerresponds to a ground-potential tens and units mark from the callinggroup of ten lines to operate switching apparatus to connect the callingline to an idle called line or trunk. The line circuits of the inventionare arranged to provide a ground-potential tens mark and abattery-potential units mark, requiring slight modication in thecontroller of the noted Leonard application, its operation however beingsubstantially the same.

.The above-mentioned and other features and objects of this inventionand the manner of attaining them will become more apparent and theinvention itself will be best understood, by reference to the followingdescription of i to TGA-10 inclusive.

understood that the invention is not so limited but may include systemsemploying many hundreds of lines. With these lines of which only oneline L1 is shown, there are provided ten common tens relays designatedTGA-1 In addition, there is employed a cutoff relay, such as relay 101and an associated rectifier element, such as 113 for each Iof the 100lines.

As shown in the'drawing, tens relay TGA-1 is associated with the tenlines in the iirst ten-line group over tip-extension conductors ET-l toET-10 and rectiiers 113 and 114, and is further associated withcontroller CR-l over tens marking conductor TM-l and control conductorC1. The individual lines in the first ten-line group are associated withsuch controller over respective mark wires 1- UM-l to 1^UM10. As will bedescribed hereinafter, controller CR-l responds to the marking on thetens mark wire 'ITM-1 and on the units mark wires 1-UM10 to control thender switch SW1 to extend a connection from a line, such as line L1, toan idle trunk OTl extending to the connector or selector switches.

Referring now to line =L1, it will be observed that thel subscriberstation S1 is associated with its individual line multiple LM-l throughthe usual main distributing frame jumper and intermediate distributingframe jumper. It will also be observed that a resistance 119 is shownbridged across the tip and ring conductors of line L1, such resistorassumed to be on the order of 10,000 ohms and being indicative lof theline leakage between the line conductors of line L1. Resistances 117 and118, being in the order of 10,000 ohms, are shown -connected torespective conductors T and R and .are indicative of the line leakagewhich may exist between either conductor to ground.

The finder switches, lindicated as SW1, are assumed to be similar to theiinder switches of the noted Leonard application and respond to controlfrom controller CR-1 to extend a connection from the calling line to anoriginating trunk.

A detailed description of the invention will be now given by describingthe` operations involved in extending av calling line, such astline L1,to an idle originating trunk OTl through line-iinding operation.

Responsive to the subscriber at station S1 on line L1 removing thereceiver (not shown), the usual line loop is closed across the tip andring conductors T and R, closing an operate circuit for the associatedtens relay 103. This circuit includes negative battery throughcurrent-limiting 'resistor 111, break contacts 2 of relay 101, the MDFand IDF jumpers, the line conductors .and station S1 subset, breakcontacts 1 of cutoff relay 101, extension wire -ET-l, rectitier 113, thewinding of the commons relay TGA, wire C1, and ground through breakcontacts 12 of tens group relay 201 of controller CR-l.

Tens relay TGA-1 operates and at its make contacts grounds the tens markwire TM-l, indicating that a call is waiting in the first ten-linegroup.

Calls from other ten-line groups may simultaneously or overlappinglyoperate their associated tens group relay to yground their associatedtens mark wire indicating call from other groups. i

f At such time, the ground on the tens mark conductors is extendedthrough the associated ones ofthe rectiiiers 26S to 275 and throughbreak contacts 2 of start relay 212 to the battery-connected winding ofpreference shift relay 213. l

Preference-shift relay 213 operates andat its make contacts 1 to 3advancen switches 241 and 242 one step and close an operate circuit forstart relay 212, in a manner described in the noted Leonard application.

Start relay 212 operates and locks independently of relay 213. At itsmake contacts I,` it operates timel relay 214 to time the interval thatthe controller' CR-I may b e held for use on one call; its breakcontacts 24 open the operate circuit of relay 213; its make contacts 4extend battery potential through resistor 128 to prepare alockingcircuit for the units test relay 215; its make contacts 6 causethe tens switch 241 to advanceacross its associated contact bank; andits make contacts 3 connect the batteryconnected winding of thetens-test relay 211 to the brush of tens switch 241 in preparation forhunting across the tens-mark conductors TM-l to TM-10.

The grounds appearing on the tens mark conductors TM-l to TM-10 areextended to. one side of the winding of the tens group relays associatedwith the tens group containing the calling lines and the other side ofthe windings of such tens group relays is connected to respectivepositions on the bank of switch 241. The brush of tens switch 241,.having battery potential from the winding of the tens-test relay 211appearing thereon, advances under control of interrupter P240 across theswitch bank, successively engaging the tens-mark wires.

Assuming the preference shift relay 213 to have advanced the brushes ofswitch 241 to position 1 and the tens mark wire TlvI-l to be grounded,the battery potential appearing on the brush is extended through thewinding of the tens group relay 201 to the ground appearing on thetens-mark conductor TM--1,` operatingv the tens group relay 201 andtens-test relay 211 in series.

Responsive to the operation of the tens group relay 201, make contacts 1to 10 extend the battery potentials from the current-limiting resistorsof each calling line in the tirst ten-line group and through` associatedones of the break contacts of unoperated relay 216 to the brushes ofunits switch 242, which responsive to the operation of relay 211advances its brush across its contact bank under control of interrupterP240. At the same time, relay 201 is locked operated and restores grouprelay TGA-1 a its contacts 12.

Responsive to the engagement of the brush ofunits switch 242 with theswitch bank contacts associatedI with the marked units wire UM-l, unitstest relay 215 operates from the noted battery potential appearing onwire UM-l and locks through current-limiting resistor 128. The notedrestoration of tens relay TGA-1 leaves the extension conductor ET-l freefrom all unnecessary currentconsuming sources, thereby increasing thepotential appearing on such wire, enhancing the operation of the unitstest relay 215.

At such time, as described in the noted Leonard application, controllerCR-l functions to cause finder switch SW1 to extend calling line L1 toan idle trunk OT1 extending to the next switching stage. As is wellknown, ground is thereupon returned on the sleeve conductor S, operatingthe cutol relay CO-1 associated with the calling line, such operationclearing the calling line of all line circuit attachments. 3

Controller CR-l is cleared out and returned to normal use in preparationfor another call, in the manner described in the Leonard application.

As is common in line circuits employing a commons tens relay such asrelay TGA-1, the leakage resistances 119 of a number of lines areeiectively in parallel, resulting in a substantially lower bridgeresistance. This lower bridge resistance, while insufficient to operatethe tens relay, often is sufcient to hold such relay operated or tosubstantially delay its release. This' noted opening of the operatecircuit of the tens relay at contacts 12 of relay 210 prevents suchtrouble conditionfrom arising.

vIt is'also common for the line leakage resistance from either conductorto ground to be of such value that current ow through the leakageresistance, indicated as resistor 117, operates the tens relay toinitiate line-finding` action. However, with the one side of the windingof the tens relay being connected to ground, such leakage resistance toground or accidental ground appearing on the line conductors cannotoperate the tens relay. The rectiers, such as 113 and 114 isolate thelines from each other as regards ground appearances on any line, to theend that a line fault on any line from ground appearing thereon does notdisable the remaining lines in the same group.

While I have -described above the principles of my invention inconnection with specific apparatus, it is to be clearly understoodl thatthis description is made only by way of example and not as a limitationto the scope of my invention.

I claim:

1. In a communication system, a switchboard, a group of lines extendingthereto and terminating thereat, means for transmitting a direct-currentpotential ofy a given polarity with respect to ground over any line tothe'- switchboard to signal a call over that line, a line' relayconnected in common between all lines and ground,

means controlled by the line relay for giving a call signal responsiveto current ilow therethrough resulting from the said direct-currentpotential on any line, and a separate impedance element connectedserially between the line relay and each line to permit operatingcurrentgto flow therethrough and through the line relay in a circuit"path between ground and the calling line, while at least' reducing thereverse flow therethrough which would tend to place the potential of thecalling line on each other line, whereby the accidental grounding of anyline other than the calling line leaves the common line relay operableover the calling line.

2. In a communication system according to claim l,

means for testing the lines individually for the said direct 4. Acommunication system according to claim 2,y

wherein the line relay is capable of being heldf operated by a lesserpotential, and consequent line current, than is required to operate it',means for isolating the calling line from the line relay, and means fortemporarily re-` storing the line relay irrespective of a callingcondition-A on any unisolated line, thereby avoiding a false calling.condition such as might otherwise obtain from foreign holding-valuepotentials on non-calling lines.

5. ln a communication system according to claiml,

each of the said impedance elements serially including ay rectifierelement so poled as to readily permit passage of the said operatingcurrent therethrough from its associated line, while resisting thereverse ow therethrough to! ground on the associated line when someother line ot the said group is the calling line. i

6. In a communication system according to claiml 2,

a separate test wire for each line, the test wire for any linecomprising an extension of the line side of the said?v separateimpedance element thereof, and means for connect ing the said test meansbetween ground and the test wires in succession, the said test meansbeing such that current n ows between ground and any connected callinglineI through the said test means in a circuit bypassing the said.impedance element thereof.

7. In a communication system according toI claim 4,'

the said means for isolating a calling line from the line said testmeans ascertaining the calling line. .Y

8. In a communication systemaccording to claim I,

each of said lines having a rst and a second conductor, and the saidmeans for transmitting a direct-current potential to signal a callincluding means for varying the conductance between the said lineconductors.

9. In a communication system according to claim 2, the said switchboardincluding switching apparatus common to the said lines for extendingconnections from calling lines towards called lines or trunks, andincluding control apparatus controllable by the said testing means foroperating a portion of the switching apparatus to extend the saidconnection from the line ascertained by the testing means as the callingline.

10. In a communication system according to claim 9, individual sleeveconductors and individual cuto relays for respective lines, meansresponsive to the said eXtension of a connection for energizing thesleeve conductor of the calling line to operate the associated cutotrelay, and means controlled by the said cutoi relay for isolating thecalling line from the said line relay.

11. In a communication system according to claim 1, groups of said linesand respectively corresponding ones of said line relays, the saidswitchboard including switching apparatus common to the said lines forextending connections from calling lines towards called lines or trunksand including control apparatus common to the said groups of lines foroperating the switching apparatus to extend the said connections, meansresponsive to the said call signal om any line relay for temporarilyindividualizing the control apparatus with such line relay andassociated group of lines, test means in the said control apparatus fortesting the lines in the last-said group for the said direct-currentpotential to select the calling line therein, and means controlled bythe said test means for operating a portion of the switching apparatusto extend the said connection from the selected calling line.

References Cited in the le of this patent UNITED STATES PATENTS2,152,889 Jedrychowski Apr. 4, 1939 20 2,193,427 Marrison Mar. 12, 19402,410,304 Powell Oct. 29, 1940

